LETTERS...

pH VALUES

Oliver Barron asked me in response to my formula in the July 87 N/L, to explain my method of checking the pH values. However, I have never actually checked the pH of my solutions. The Value in my process are given in the original formula from the B.J. Annuals, 1983, for most baths, earlier issues for other baths. I believe the pH values can be altered in the ways:-

For 1st. & Col. Devs. To raise the pH add quantities of 10% sodium hydroxide solution. To lower the pH, add quantities of 10% sulphuric acid solutions. Adding 5 mls. of solution to 1 Litre of 1st. or Col. Dev. alters the pH by 0.1 units.

For Bleach & Fixer. The pH of thee solutions is closer to neutral, so the acid and alkali used for control purposes are weaker. To raise the pH 10% Ammonia solution is used; to lower the pH . 10% acetic acid is used.

I should stress that I have not ever actually tried these out; I have relied on the formula giving a pH within the defined limits. In any event, I feel the pH in the Bleach & Fixer are not so critical, as I have learned from other Club members that there are quite a number of bleach and fixer recipes in use, all giving good results, but with different composition and therefore likely to be slightly different in pH.

I think pH is much more important in the 1st. & Col. Developers and this is a more profitable area for experimentation. As an after thought, I have found quite significant variations in colour rendering by altering (a) the thiocyanate content of 1st. Dev. - less thiocyanate shifts colour away from cyan and more towards red. (B) Citrazinic acid in the Col. Dev. More citrazinic lowers contrast and shifts colour away from blue towards yellow.

The recipe I use are a modification (using (a) and/or (b) above) of the 1983 B.J. formula, but I have not tried much tinkering with the pH. It is certainly true different batches of chemical produce colour variations, as I have found a new batch of CD4 produced a slight blue cast in the slides, compared to the old batch.

Derek Foster (Area 13).

FRANK REMARKS Since writing the `Formula for E6 Success` I have carried out processing my holiday films and using a ferric EDTA bath. I was far from satisfied. The leaders appeared to be grey, i.e. lightly fogged. The colours were nowhere as dense as previously though, this could be due to something else entirely. I have subsequently returned to my previously outlined method and obtained brilliant results, so it is something to do with the bleach.

I would advise members to carefully check their colour developer, especially pH value. The problem chemical is the tri-sodium Phosphate. If it is fresh it is OK. If it has been kept in storage for some time, it has the power to react with the carbon dioxide in the atmosphere and tends to become acid, thus throwing out the carefully balanced pH value of the Col. Dev.

It may be some bearing on my results with my formula that I had both my Olympus cameras serviced before carrying out this work, to ensure consistent exposures.

Finally, I went to the Laboratory Exhibition and enquired about pH meters. Believe it or not, the CP meters are made by an Italian firm called `Hanna` and are being sold by Whitman`s and Hanna as well.

A tip on using these instruments - do not immerse them more than one inch into the solution. When going from one solution to another, wash them in distilled water and if drying them, use Methanol. Preferably, use one instrument for one solution only, to avoid contamination.

Frank White (Area 13).